Cambridge IGCSE™
CHEMISTRY
0620/31
Paper 3 Theory (Core)
May/June 2023
MARK SCHEME
Maximum Mark: 80
Published
This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the
examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the
details of the discussions that took place at an Examiners’ meeting before marking began, which would have
considered the acceptability of alternative answers.
Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for
Teachers.
Cambridge International will not enter into discussions about these mark schemes.
Cambridge International is publishing the mark schemes for the May/June 2023 series for most
Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some
Cambridge O Level components.
This document consists of 13 printed pages.
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0620/31
Cambridge IGCSE – Mark Scheme
PUBLISHED
Generic Marking Principles
May/June 2023
These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the
specific content of the mark scheme or generic level descriptors for a question. Each question paper and mark scheme will also comply with these
marking principles.
GENERIC MARKING PRINCIPLE 1:
Marks must be awarded in line with:



the specific content of the mark scheme or the generic level descriptors for the question
the specific skills defined in the mark scheme or in the generic level descriptors for the question
the standard of response required by a candidate as exemplified by the standardisation scripts.
GENERIC MARKING PRINCIPLE 2:
Marks awarded are always whole marks (not half marks, or other fractions).
GENERIC MARKING PRINCIPLE 3:
Marks must be awarded positively:





marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond
the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate
marks are awarded when candidates clearly demonstrate what they know and can do
marks are not deducted for errors
marks are not deducted for omissions
answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the
question as indicated by the mark scheme. The meaning, however, should be unambiguous.
GENERIC MARKING PRINCIPLE 4:
Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level
descriptors.
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PUBLISHED
May/June 2023
GENERIC MARKING PRINCIPLE 5:
Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may
be limited according to the quality of the candidate responses seen).
GENERIC MARKING PRINCIPLE 6:
Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or
grade descriptors in mind.
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Cambridge IGCSE – Mark Scheme
PUBLISHED
May/June 2023
Science-Specific Marking Principles
1
Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks
should not be awarded if the keywords are used incorrectly.
2
The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for
any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored.
3
Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation from other
syllabus terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection).
4
The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically
correct way, the candidate should be awarded these subsequent marking points. Further guidance will be included in the mark scheme
where necessary and any exceptions to this general principle will be noted.
5
‘List rule’ guidance
For questions that require n responses (e.g. State two reasons …):





The response should be read as continuous prose, even when numbered answer spaces are provided.
Any response marked ignore in the mark scheme should not count towards n.
Incorrect responses should not be awarded credit but will still count towards n.
Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be
awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this
should be treated as a single incorrect response.
Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.
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6
Cambridge IGCSE – Mark Scheme
PUBLISHED
May/June 2023
Calculation specific guidance
Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show
your working’.
For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded
by the examiner to the number of significant figures given in the mark scheme. This may not apply to measured values.
For answers given in standard form (e.g. a  10n) in which the convention of restricting the value of the coefficient (a) to a value between 1
and 10 is not followed, credit may still be awarded if the answer can be converted to the answer given in the mark scheme.
Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded.
Exceptions to this general principle will be noted in the mark scheme.
7
Guidance for chemical equations
Multiples / fractions of coefficients used in chemical equations are acceptable unless stated otherwise in the mark scheme.
State symbols given in an equation should be ignored unless asked for in the question or stated otherwise in the mark scheme.
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Examples of how to apply the list rule
State three reasons … [3]
A
1 Correct

2 Correct

3 Wrong

B
1 Correct, Correct
(4 responses)
2 Correct

3 Wrong
ignore
C
1 Correct

(4 responses)
2 Correct, Wrong
, 
, 
3 Correct
ignore
D
1 Correct

(4 responses)
2 Correct, CON (of 2.)
3 Correct
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2
, (discount 2)
3
2
2

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Cambridge IGCSE – Mark Scheme
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E
1 Correct

(4 responses)
2 Correct

3 Correct, Wrong

F
1 Correct

(4 responses)
2 Correct

3 Correct
CON (of 3.)
1 Correct

(5 responses)
2 Correct


ignore
ignore
H
1 Correct

(4 responses)
2 Correct

3 CON (of 2.)
Correct
1 Correct

(4 responses)
2 Correct

© UCLES 2023
3
2
(discount 2)

I
3 Correct
CON (of 2.)
2

(discount 3)
G
3 Correct
Correct
CON (of 4.)
3
2

(discount 2)
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Question
Answer
May/June 2023
Marks
1(a)
N
1
1(b)
He
1
1(c)
I
1
1(d)
O
1
1(e)
Fe
1
1(f)
Al
1
Question
Answer
Marks
2(a)(i)
values between –100 °C and +58 °C (inclusive of these values)
1
2(a)(ii)
values between 3.20 and 10.0 (inclusive of these values
1
2(a)(iii)
gas
1
–10 °C is above the boiling point
1
2(b)(i)
displacement
1
2(b)(ii)
chlorine is more reactive than iodine / iodine is less reactive than chlorine
1
2(c)
configuration as 2,8,7
1
2(d)
damp litmus paper (1)
2
bleaches (1)
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Question
3(a)
Answer
May/June 2023
Marks
oxygen
1
3(b)(i)
sewage / microbes
1
3(b)(ii)
deoxygenate (the water) / remove oxygen (from the water)
1
3(c)(i)
hydrogencarbonate
1
3(c)(ii)
ammonium
1
3(c)(iii)
0.44 (mg)
1
3(d)(i)
(substance that is) chemically combined with water
1
3(d)(ii)
heat
1
2(H2O) (1)
2
3(e)
H2 (1)
Question
4(a)
Answer
atom(s) with the same number of protons(1)
Marks
2
different numbers of neutrons (1)
4(b)
protons: 16 (1)
3
neutrons: 20 (1)
electrons: 18 (1)
4(c)(i)
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S + O2 on left horizontal line AND SO2 on right horizontal line
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1
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Cambridge IGCSE – Mark Scheme
PUBLISHED
Question
May/June 2023
Answer
Marks
4(c)(ii)
the energy of the reactants is greater than the energy of the product / the energy of S + O2 is greater than the energy of
SO2
1
4(c)(iii)
surroundings
1
4(d)(i)
right hand electrode labelled cathode (1)
2
electrolyte labelled (1)
4(d)(ii)
4
product at positive electrode: oxygen (1)
observations at positive electrode: bubbles (1)
product at negative electrode: hydrogen (1)
observations at negative electrode: bubbles (1)
4(e)
3
sodium sulfate (1)
carbon dioxide (1)
water (1)
4(f)
colourless
Question
5(a)
Answer
1 mark each for any two of:




© UCLES 2023
1
Marks
2
iron has a high(er) melting point / boiling point
iron has a high(er) density
iron is strong(er)
hard(er)
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Question
5(b)
Answer
to provide heat / increase temperature (1)
May/June 2023
Marks
2
to produce carbon dioxide (from the combustion of carbon) (1)
5(c)(i)
mixture of a metal with another element
1
5(c)(ii)
harder / stronger / more resistant to corrosion
1
lead<nickel<iron<magnesium (2)
2
5(d)
if 2 marks not scored: 1 mark for 1 pair adjacent reversed OR
magnesium<iron<nickel<lead
Question
Answer
Marks
6(a)(i)
1.0 (mol / dm3)
2.0 (mol / dm3)
1.5 (mol / dm3)
1
6(a)(ii)
takes longer time / time increases
1
6(a)(iii)
takes shorter time / time decreases
1
6(b)
filtration
1
6(c)
4th box down ticked (sodium nitrate)
1
Question
Answer
Marks
7(a)(i)
circle around one or both COOH groups
1
7(a)(ii)
C5H6O4
1
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Question
7(a)(iii)
Answer
orange (1)
May/June 2023
Marks
2
to colourless (1)
7(b)
(family / group of similar) compounds with similar chemical properties (1)
2
having the same functional group (1)
7(c)
magnesium ethanoate (1)
2
hydrogen (1)
7(d)
88 (2)
2
If 2 marks not scored 1 mark for 32 (for O)
OR 8 (for H)
7(e)
ethene (1)
2
steam / water (1)
Question
8(a)
Answer
1 mark each for any 2 of:




Marks
2
poor thermal conductor / poor conductor of heat
not malleable / brittle
not ductile
low melting point / low boiling point
8(b)(i)
car engines
1
8(b)(ii)
respiratory problems / photochemical smog
1
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Question
8(c)(i)
Answer
pair of electrons (1)
May/June 2023
Marks
2
(electron(s) shared) between two atoms (1)
8(c)(ii)
3 dot-and-cross bonding pairs between each H and N and no extra electrons on H (1)
2
Two non-bonding electrons on N (1)
8(c)(iii)
pH 10
1
8(c)(iv)
1 mark each for any 3 of:
 evaporation (of ammonia)
 diffusion (molecules)
 molecules in (constant) movement / molecules
collide / hit / molecules travel / molecules move (rapidly)
 (movement of) molecules is random / in every direction
 molecules spread out / molecules mix
 molecules hit / reach litmus paper
 (molecules spread) from higher concentration to lower concentration / down concentration gradient
3
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